: The investigators propose to study inhibition of HIV replication in vitro and in vivo by single chain Fv antibodies (SFv) against HIV proteins. They have found that SFv (#Aw) against HIV-1 integrase (IN) inhibits virus replication better than SFv vs. the other HIV proteins we have tested. To deliver SFv genes, they will use a unique gene transfer system that we have developed: T-antigen-depleted SV40 effectively delivers transgene expression in vitro and in vivo to bone marrow cells and to unselected, resting human lymphocytes. SV-Aw delivers very high levels of the HIV-inhibitory SFv, Aw, to cultured human T cells. This transduction system will be used to inhibit HIV-1, SHIV and SIV in vitro and in vivo. Their group of collaborators will apply test systems that they have developed: a gene transfer vector that yields high level transgene expression on inoculation in vivo, intracellular SFv that inhibit HIV-1 in vitro, a mouse system to study progression and inhibition of HIV infection in bone marrow-derived cells, and a primate system to test SHIV and SIV infection and its inhibition. The applicants hypothesize that intracellular anti-IN SFv can be transferred by SV-40-derived vectors sufficiently to protect against HIV and SIV infection in vitro and in vivo. To test this hypothesis, they will assess the ability of SV40-delivered SFv to inhibit HIV infection of human T lymphocytes in vitro by testing SV-Aw, as well as SV40-delivered SFv vs. HIV rev and reverse transcriptase. They will apply these vectors to study inhibition of HIV infection by transduction ex vivo, and in vivo, in SCID-hu mice. These studies will identify aspects of SV40-delivered Aw expression that need to be improved, e.g., increasing levels, stability and/or longevity of transgene expression. The applicants will modify transfer vectors accordingly. These enhanced vectors will be tested first in vitro then in vivo vs. HIV-1 in human cells and SCID-hu mice. Because of the importance of studying this approach to HIV inhibition in an experimental system resembling human AIDS, they will use rhesus macaque monkeys to study the ability of SV-40-delivered SFv to inhibit immunosuppressive lentivirus infection in primates. Existing anti-HIV rev SFv will be used to study inhibition of SHIV-4 infection in monkey bone marrow cells, and , if successful, in vivo. They are also currently developing SFv vs. SIV IN, RT and rev for use against SIV in vitro and in vivo. SV40-based gene transduction has great promise, particularly when combined with intracellular SFv, in inhibition of HIV infection.